In 2009, a male polar bear carries the head of a polar bear cub it killed about 200 miles north of the Canadian town of Churchill. REUTERS/Iain Williams

December 12, 2011

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Is global warming driving polar bears to cannibalism? It certainly appears that way, say wildlife experts. And a jarring set of photographs published in the journal Arctic has provided a rare piece of evidence to support the theory. Here's what you should know:

What happened?Wildlife photographer Jenny Ross was on a boat floating through a stretch of water in the Svalbard archipelago when she came across an adult polar bear tearing into what she thought was a seal. But upon closer inspection, it turned out to be the fresh carcass of a juvenile polar bear cub. "It's been known that polar bears do kill — and sometimes eat — their own kind," says Rob Waugh at Britain's Daily Mail. "But the behavior appears to be on the increase."

Are wildlife experts sure the adult killed the cub?"The kill method used by the adult was exactly the same as polar bears use on seals," says Jonathan Amos at BBC News — "sharp bites to the head." Another bear was also present in the area, which Ross speculates "might have been the mother of the dead juvenile."

Why do polar bears kill their own?Simple: They're hungry. And that hunger may have something to do with diminishing ice masses in the arctic. As "the area of sea ice that polar bears can use for hunting declines, progressively fewer seals are accessible to the bears," says Ross. And "therefore the bears' hunting success likely decline as well."

So climate change is to blame?It plays a part, many scientists say. But here's the real "twist in this story," says Tori Floyd at Yahoo. "The practice isn't just happening in the wild: There have been odd cases of polar bears killing and eating younger cubs in controlled environments, too." In 2008, for example, a zoo in Nuremberg, Germany, reported that a mother polar bear ate one of her own twin cubs. Says one Inuit leader, "an adult polar bear eating a cub is actually quite a normal occurrence."